1. Field of the Invention
The present invention relates to a film supply device that transfers the rotation of a motor to a winding shaft through a planetary clutch mechanism.
2. Description of Related Art
FIG. 7 shows an example of a camera film supply device. With this device, the rotation of a motor 2 is transferred to a sun gear (central gear) 12 of the planetary clutch mechanism through gears 4, 6, 8 and 10. The planetary clutch mechanism has a planetary lever 14 that rotates about the axis of rotation of the sun gear 12. A planetary gear 16 revolves about the sun gear 12 supported by the planetary lever 14. A regulating shaft 18 extends from the axis of rotation of the planetary gear 16. The regulating shaft 18 inserts into an elongated hole 20a in a body base plate 20 to restrict the range of rotation of the planetary lever 14 to a fixed angle. A compression spring (not shown) is mounted between the planetary lever 14 and either the sun gear 12 or the planetary gear 16. The planetary lever 14 rotates integrally with the sun gear 12 under the frictional force of the compression spring.
When the motor 2 rotates in the direction labelled R1, the planetary gear 16 and gear 50 enmesh (as shown in FIG. 8A), and the rotation of the motor 2 is transferred to a spool gear 54 through a gear 50 and a gear 52. This causes a winding spool 56 to rotate in the direction labelled R3 in FIG. 7, and wind the film 92 drawn from the cartridge 90. The winding spool 56 is formed as an integral unit with the spool gear 54. When the motor 2 rotates in the direction labelled R2, the planetary gear 16 enmeshes with gear 60. A rewinding fork 70 is rotated in the direction labelled R4 through gears 62, 64, 66 and 68. The rewinding fork 70 rewinds film 92 into the cartridge 90.
During the winding of the film 92, perforations 94 in the film 92 that pass by a reflective optical sensor 80 are detected. The number of passing perforations 94 controls the rotation of the motor 2. For example, when there are eight perforations 94 for a single photo frame, the motor 2 is driven to rotate at full speed until six of the perforations 94 have passed. Braking of the rotation of the motor 2 is then performed so that the film 92 stops at the point where the eighth perforation 94 is detected. Braking of the motor 2 can be performed by applying a reverse current for a short period of time (pulse current).
The film supply speed is large when the motor 2 of the conventional film supply device rotates at full speed. This causes the planetary gear 16 to separate sometimes from the gear 50 when the motor 2 is braked suddenly. From the full speed rotation R1 state as shown in FIG. 8A, the motor 2 enters the braking section (the section after the sixth perforation has passed in the example). A negative angular acceleration is created from the gear 4, the gear 6, the gear 8, the gear 10, and the sun gear 12 to the planetary gear 16 accompanying the motor 2 braking. The gear 50, the gear 52 and the spool gear 54 try to maintain rotation because of inertia. Consequently, the peripheral speed of the gear 50 is greater than the peripheral speed of the planetary gear 16. Therefore, the planetary gear 16 is repelled and separates from the gear 50, as shown in FIG. 8B. When the planetary gear 16 separates from the gear 50, film supplying cannot be controlled even if the motor 2 is controlled. Thus, stopping the film 92 at the desired position is not possible.
There is no alternative to eliminating rapid braking of the motor 2. Consequently, to prevent the described problem, either lowering the number of rotations of the motor 2 at full speed or lengthening the braking section is required. However, these countermeasures eliminate high speed film supplying. Further, the time needed to wind one frame of the film 92 becomes longer.
An additional problem exists because conditions under which the planetary gear 16 is repelled vary widely. The conditions vary widely because of fluctuations in the film supply speed and mechanical errors in the planetary clutch mechanism. Thus, accurate braking control settings are difficult to realize.